Electric furnace



M. UNGER ELECTRIC FURNACE Filed June l, 1928 Dec. 23, 1930.

- x/ x fl /W W Inventor* H is Attorney Patented Dec. 23, 1930 UeNlTED STATES PATENT OFFlCE MAGNUS UNGEB, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPOBATION OF NEW YORK EQEGTBIG FURNACE i Application filed June`1,

My invention relates to electric 'fur-nanes, more particularly to electric metal melting zfrnaces, and has for'itsobject a rugged and eflioient furnace Construction whereby leakage of the molten metal is prevented and provision, made for relative eXpansion of various parts due to increase in temperature.

More *specifically my invention has par ticular reference to electric metal melti'n :turnaces in which all or part of the meta being heated forms a' closed secondary in which heating currents are induced from a primary winding arranged within the secondary. In this type of furnace the metal is contained in a crucible which is ordinarily for-med by ramming a suitable refractory material in plastic formin a suitahly sha ed zoli, after which the crucible is suita lly i re i It has been found that refractory crucibles, especially those ormed by ramming the refractory material in a mold, sometimes develop Cracks due to unequal expansion :from changes `in temperature or due to local heating and cooling, resulting in leakage of molt'en metal. ,In induction furnaces there is the danger that the mclten metal escaping 'through such cracks may form secondary loops and thus become heated by induced current. The escaping metal is thus kept liquid and tends to run further until eventually a serious run-out may take place. Furthermore, in ring type furnaces in which the crucible containing the molten metal surrounds a refractory tube which in turn surrounds a primary heating coil, the crucible 'tends to eXpand on heating and thus a space is often formed between the crucible and the tube which surrounds the primary winding. Metal leaking into this space may :form a secondary circuit and cause trouble.

In accordance with my invention I arrange a layer of powdered or granular refractory material ,adjacent the crucible so that in case a metal leak occurs through a crack in the linin the metal'will he stopped when it reachest e layer of granular material. The powdered or granular material 50 also allows relative expansionand contrac- 1928. t Serial m. m st.

tion of the crucible and the heat insulating walls surrounding it.

In carrying out my invention further, I have provided flexible members :tor taking care of relative expansion and contraction between certain refractory heat insulating walls of the furnace and a surrounding metallic shell or casin For a more comp ete understanding of my invention, reference may he had to the accompanying drawing in which Fgy 1 is a sectional elevaton of a ring type furnace embodying my invention; Fig. 2 is a sectional elevaton showing my inventionapplied to a furnace of another type and Fig. 3 is an enlarged view taken on line 3--3 of Fig. 2 looking in the direction of the arrows.

` Referring to the drawing, I have shown my invention in Fig. 1 as applied to a horizontal ring type induction furnace comprising a primary winding 10 surrounding a core 11, and a crucible providing a channel 12 for holding the molten metal 13 which acts as a closed secondary in which Currents are induced by the primary winding 10. The chan nel 12 is formed in an annular crucible 14 which may be made from a suitable refractory material, such as a mixture of 'fused magnesia, calcined `magnesia and. a binder such as magnesium sulphate, as described in Patent No. 1,444:,527 to Scharschu, dated Feb. 7, 1925. These materials are mixed in granulated or powdered form, suilicient water being added to make a plasticmixture and the mass thus formed is rammed-in place in a suitable mold which defines the crucible 14; with its channel 12. surrounding and also immediately underneath the crucible 14 is a layer of suitable refractory hoat insulating material 15 such as fire brick. A refractory member 16 is provided, forming a cover for the upper surfaces of the crucible 14 and the refractory layer 15, and this cover member 16 may contain a groove 17 in registering relation withthe channel 12. For strengthening purposes the cover member 16 and the upper and outer edge of the layer 15 may be bound with metallic strips 18, L-shaped in cross section.

A metallic tubular'inember 19 surrounds the primary winding 10 wound on one leg of the core 11 and between this tubular member 19 and the crucible 14 is a layer 20 of refractory, granular material, such as fused magnesia grains; The granular material 20 is rammed and packed to form a very dense mass, and to provide means for packing this material tightly between the tubular member 19 and the crucible 14, I provide a series of non-magnetic tubes 21, arranged vertically, approximately midway between the tubula' member 19 and the crucible 14. The packng of the granular material 20 is accomplished while the metal 13 and crucible 14 are being heated, by Vibrating the tubes 21 continuously by any suitable vibrator, not shown, 'such as used in foundries. This assures the compacting of the material tightly against the crucible after it has been heated to operating temperatures, and subsequently during operation whereby leakage of molten metal through any cracks which may be formed in the crucible will be stopped. While the furnace is in operation the tubes 21 also serve the purpose of cooling any metal leaks occurring in the crucible by the passing of a cooling medium, such as air, water, or air with atomized water, through the tubes.

Between the outer periphery of the crucible 14 and the refractory layer 15 I provide another layer 22 of the granular material such as used in the layer 20. The space between the crucible 14 and the layer 15 is filled with the granular material 22 while the crucible 14 is cold and this material 22 serves to take up the difference-in expansion between the crucible 14 and the layer 15 when the crucible is heated. The crucible 14 has high heat conductivity and hence it is general practice to use an outer layer 15 of a material having low heat conductivity. consequently, when the furnace is heatecl the crucible will expand more than the refractory layer 15, and one purpose of the layer 22 of granular material is to serve as a butter to take up the difference of expansion so that the danger of breaking the refractory layer 15 will be avoided. It is to be understood that the material 22 is not packed as densely as the material forming layer 20. `When 'the fun nace is in operation, if a crack should develop in the crucible 14, causing the metal 13 to leak therethrough, the flow of the metal will stop when the metal comes to the junction of the crucible and the granular material forming the layers 20 or 22.

l'n Figs. 2 and 3 I have shown my invention as applied to a furnace of the type disclosed in a patent in my name No., 1528375, dated May 10, 1927. This fur-hace comprises an inner heat insulated crucible 23 which is shaped to provide a reservoir 24 for the metal and an annular chamber 25 in which a por-` tion oi: the molten metal *forms a closed. see ondary for a primary winding 26 assoeiated therewith. The annular channel 25 is horizontally arranged, i. e. with its axis substantially vertical at one side of the reservoir 24, a slight distance above the bottom of the reservoir. It is connected with the recervoir through ducts 27 and 28 provided in-the refractory material of the crucible. The crucible 23, similar to crucible 14 of Fig. 1, is made from a suitable refractory material such as a mixture of fused magnesia, calcined magnesia and a binder such as magnesium sulphate. This material is rammed in place around a suitable core which defines the reservoir 24, the channel 25 and the ducts 27 and 28. Preferably a hollow metallic core is used which can subsequently be filled with molten steel and melted out as described in Kny aforementioned Patent No. 1,628,375. surrounding 'the crucible23 is a layer of suitable refl-actory, heat insulating material 29, such as fire brick or diatomaceous earth, the whole being enclosed by a metallic casing 30. A metallic shell 31 surrounds the furnace and a member 32 of refractory material forms a cover for the reservoir 24. The cover member 32 may be supported in any suitable manner and is shown as resting on angle irons 33 attached to the outer shell 31. Angular rings 34 serve to strengthen the ou'ter shell 3.

A metallic, tubular member 35 surrounds the primary windin'g 26 and between this tubular member 35 and that part of the crucible 23 containing the channel 25 is a layer of packed, granular material 36 similar to the material forming layers'20 and 22 shown in Fig. 1. This layer of granular material 36 also extends between the bottom of the crucible 23 and the refractory material 29 and also surrounds the outer portion of that part of the crucible containing the channel 25. Non-magnetic cooling tubes 37 are provided, as in 1, and these tubes serve the dual purpose of aiding in packing the granular material 36 and in cooling this material when the furnace is in operation in a manner similar to that used in the furnace shown in Fig. 1.

:in order to take care of expansion of the refractory material when the furnace is heated I have provided bufng means, shown more clearly in Fig. 3. Between the metallic casing 30 and the outer shell 31 E place a plurality of corrugated, metal sheets 38, mounted vertically. Due to the resilience of these sheets 38 the expansion of the refractory material and the metal casing 30 will be absorbed.

The furnace is preferahly :mounted on suitable rockers 39 which rest on trasha 40, and it may be tilted by means of a suitable hydraulic motor 41 in order to pour metal from the furnace. This is descrihed and explained more clearly in my Patent Ne. 1,628,575, hereinbefore referred to,

Should metal leaks occur in the bottom of the crucible 23 or in that part of the crucible -containing the channel 25, the flowing metal will be stopped when it reaches thejunction of the crucible 23 and the packed, granular material 36. It will be observed that the granular material 20 and 22 of the furnace shown in Fig. 1 and the granular material 36 of the furnace shown in Fig. 2 perform two functions, that is, the granular material as'sists in absorbing expansion between the cruciblesand the outer refractory layer and, secondly, the gra'nular material serves to sto metal leaks occurring in the crucibles.

(Fertain features of my invention disclosed in this application relating to the method of packing a furnace crucible are described and claimed in a copending application, Serial Noi &45,477, filed April 18, 1930, which application is a division of this application.,

go lVhile I have described my invention as embodied in concrete form and Operating in a specific manner in accordance with the provsions of the patent statutes, it should be understood that I do not limit my invention 5 thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my nvention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a metal melting furnace, the combination with a crucble for the charge, of a heat insulating wall substantially surrounding said crucible, a metal casng surrounding said wall and spaced therefrom and a plurality of metallic corrugated members between said casng and said wall.

2. In an induction furnace, the combination with a crucible for the charge comprising a refractory reservoir and an annular member containing a channel in which a portion of the charge forms a closed secondary, of a heat insulating wall substantially surrounding said reservoir and said annular member, a metal casing surrounding said wall and spaced therefrom, and a plurality of :metallic corrugated sheets between said casingand said wall.

3. In a metal melting furnace, the combination with a crucible for the charge of a heat insulating wall substantially surrounding said crucible, a metal casing surrounding said wall and spaced therefrom and a 55 metallic corrugated member between said casing and said wall.

Inwitness whereof I have hereunto set my hand this 29th day of May, 1928.

MAGNUS UNGER. 

